Serological and molecular tools for the evaluation of malaria transmission blocking vaccines

Malaria transmission blocking vaccines (TBV) have been prioritized as an intervention to facilitate malaria elimination, but tools are required to support roll-out and evaluation. This thesis presents research that aids development of pre-fertilization TBV candidate 10C (amino acids 159-428 of Pfs48/45). Gametocytes must be detected to identify the infectious reservoir and support mosquito infectivity studies. I proposed filter papers as a novel, cost effective, practical approach for collection and detection of mRNA in low density gametocytes. Comparing 3 filter papers, 2 RNA extraction methods and 2 molecular detection techniques, I concluded Whatman 903 and Whatman 3MM filter papers, combined with guanidine based nucleic acid extraction and detection using QT-NASBA, were operationally most appealing and most sensitive. To identify natural recognition to 10C and 230CMB (a vaccine candidate including amino acids 444-730 of Pfs230), cross sectional surveys were performed sampling school children (n=510) in 3 countries. I demonstrated naturally exposed individuals had antibodies against 10C and 230CMB which displayed age dependent acquisition (p<0.03). Supportive datasets demonstrated 10C and 230CMB antibodies are significantly associated with >90% transmission reducing activity (TRA) (p<0.003). To assess the TRA of 10C-immunized rats against genetically diverse parasites, I sampled venous blood from naturally infected participants in Burkina Faso (n=53), and performed direct membrane feeding assay combined with serum replacement using European control serum spiked with IgG from 10C vaccinated rats. I demonstrated 10C vaccine induced IgG significantly reduced transmission in 4/5 participants who were infectious and infected >2 mosquitoes. This resulted in 80.9-100% reduction in oocyst prevalence (p<0.042), and 85.2-100% reduction in oocyst density (p<0.023). My research identified an attractive combination of tools for detecting low density gametocytes to facilitate sampling in remote field settings. I advanced progress of 6 10C vaccine candidate by indicating antibodies are acquired following natural malaria exposure and are associated with functional TRA.